Prior research in rodents suggests that living without exposure to environmental complexity leads to physiological changes in the brain that carry heavy functional costs. In comparison to rats, non-human primates are characterized by complex social behavior and cognitive capacity. They interact with their environment in intricate ways and are therefore likely to have greater requirements with respect to environment for optimal functioning. Housing monkeys in standard laboratory cages may have an even greater negative impact on their brain than the decreased neuronal survival shown by my prior work in rats. Our laboratory has built a new marmoset facility and my general intent for the next several years is to characterize experiential influences on neurogenesis and dendritic architecture in adult marmosets. The proposed experiments will correlate several indices of brain plasticity in this species with the level of environmental complexity and determine whether the effect is graded. If living in an enriched environment alters brain structure in the adult marmoset, then individual variables responsible for the effect will be identified. This work will begin to characterize the effects of living in different environments on structural plasticity in adult primates, and it will create the basis for studying animals in laboratory conditions that are free of the potential confounds of variable housing. [unreadable] [unreadable]